1. Technical Field of the Invention
Implementations consistent with the principles of the invention generally relate to the field of battery technology, more specifically to three-dimensional energy storage systems and devices, such as batteries and capacitors, and methods of manufacturing thereof.
2. Background
Existing energy storage devices, such as batteries, fuel cells, and electrochemical capacitors, typically have two-dimensional laminar architectures (e.g., planar or spiral-wound laminates) with a surface area of each laminate being roughly equal to its geometrical footprint (ignoring porosity and surface roughness).
FIG. 1 shows a cross sectional view of an existing energy storage device, such as a lithium-ion battery. The battery 15 includes a cathode current collector 10, on top of which a cathode 11 is assembled. This layer is covered by a separator 12, over which an assembly of an anode current collector 13 and an anode 14 are placed. FIG. 2 shows another embodiment of a lithium-ion battery where the cathode current collector 10 is coated on both sides with a cathode active paste 11, and the anode current collector 13 is coated on both sides with an anode active paste 14 and separator layers 12 are placed on both sides of the anode active pastes. This stack can be rolled, stuffed into a can, and filled with electrolyte to assemble a battery. During a charging process, lithium leaves the cathode 11 and travels through the separator 12 as a lithium ion into the anode 14. Depending on the anode 14 used, the lithium ion either intercalates (e.g., sits in a matrix of an anode material without forming an alloy) or forms an alloy. During a discharge process, the lithium leaves the anode 14, travels through the separator 12 and passes through to the cathode 11.
Three-dimensional batteries have been proposed in the literature as ways to improve battery capacity and active material utilization. It has been proposed that a three-dimensional architecture may be used to provide higher surface area and higher energy as compared to a two-dimensional, laminar battery architecture. There is a benefit to making a three-dimensional energy storage device due to the increased amount of energy that may be obtained out of a small geometric area.
The following references may further help to illustrate the state of the art, and are therefore incorporated by reference as non-essential subject matter herein: Long et. al., “Three-Dimensional Battery Architectures,” Chemical Reviews, (2004), 104, 4463-4492; Chang Liu, FOUNDATIONS OF MEMS, Chapter 10, pages 1-55 (2006); Kanamura et. al., “Electrophoretic Fabrication of LiCoO2 Positive Electrodes for Rechargeable Lithium Batteries,” Journal of Power Sources, 97-98 (2001) 294-297; Caballero et al., “LiNi0.5Mn1.5O4 thick-film electrodes prepared by electrophoretic deposition for use in high voltage lithium-ion batteries,” Journal of Power Sources, 156 (2006) 583-590; Wang and Cao, “Li+-intercalation Electrochemical/Electrochromic Properties Of Vanadium Pentoxide Films By Sol Electrophoretic Deposition,” Electrochimica Acta, 51, (2006), 4865-4872; Nishizawa et al., “Template Synthesis of Polypyrrole-Coated Spinel LiMn2O4 Nanotubules and Their Properties as Cathode Active Materials for Lithium Batteries,” Journal of the Electrochemical Society, 1923-1927, (1997); Shembel et. al., “Thin Layer Electrolytic Molybdenum Oxysulfides For Lithium Secondary Batteries With Liquid And Polymer Electrolytes,”5th Advanced Batteries and Accumulators, ABA-2004, Lithium Polymer Electrolytes; and Kobrin et. al., “Molecular Vapor Deposition—An Improved Vapor-Phase Deposition Technique of Molecular Coatings for MEMS Devices,” SEMI Technical Symposium Innovations in Semiconductor Manufacturing (STS: ISM), SEMICON West 2004, 2004 Semiconductor Equipment and Materials International. 
Three-dimensional batteries can employ monolithic electrodes. For example, FIG. 3 shows some designs of three dimensional batteries. In FIGS. 3A-3D, cathodes 30 and anodes 31 protrude from the same backplane and are alternating in a periodic fashion. The electrodes can be monolithic. If silicon is used as the anode, then a monolithic structure can be readily assembled using well-known techniques such as deep reactive ion etching. However, use of such silicon anodes may be problematic with conventional battery electrolytes such as lithium hexafluorophosphate (LiPF6) in a mixture of ethylene carbonate and diethyl carbonate. Specifically, the silicon anode may show a high impedance during the first charge which would lead to a need to limit the charging rate to a low level in order to avoid lithium metal deposition. This low charging rate would greatly increase the time required to charge the battery and hence the manufacturing cost.
It would be desirable to make three-dimensional electrochemical energy devices with silicon anodes that provide significantly higher energy and power density, while addressing the above issues or other limitations in the art.